Anyone who is away from the UK for longer than 3 months needs to make their own healthcare arrangements in the country that they have travelled to. It is not appropriate for a UK doctor to be sending prescriptions to patients who live abroad. More information can be found via these links.
https://www.nhs.uk/using-the-nhs/healthcare-abroad/moving-abroad/planning-your-healthcare/
https://www.nhs.uk/using-the-nhs/healthcare-abroad/healthcare-when-travelling-abroad/